A DETAILED GRAVITY SURVEY OF A PULL-APART BASIN IN NORTHEAST SOUTH CAROLINA

Geomorphic analyses reveal an anomalous pattern of river trends termed zones of river anomalies (ZRA) within the South Carolina Coastal Plain (SCCP) extending north to Virginia (Marple and Talwani, 2000). The ZRA is divided into ZRA-south, central, and north (ZRA-S, C, and N), with a right-stepping en echelon pattern, which Marple and Talwani (2000) have labeled the East Coast Fault System (ECFS). The nature of the ECFS, primarily the right-lateral motion and right-stepping pattern, is conducive to the formation of pull-apart basins at the step-over regions. The region between the northern ZRA-S and the southern ZRA-C is overlain by swamp material with steep bounding surfaces suggesting the presence of a pull-apart basin. To delineate the geometry and depth configuration of the proposed pull-apart basin, we carried out a detailed gravity survey. Gravity data were acquired with a station spacing of 2 to 4 km and vertical control from spot elevations on 7.5’ quadrangle maps. These data were interpreted in conjunction with available aeromagnetic and limited subsurface data. The southern end of the ZRA-S lies within the Middleton Place Summerville Seismic Zone, the location of historic and continuing seismicity in the SCCP. The gravity data, as well as knowledge of the ages of post Cretaceous sediments, provide a foundation for our tectonic interpretation, allowing us to infer current and prehistoric rates of neotectonic activity. The unique configuration of the pull-apart basin at the step-over region between the ZRA-S and ZRA-C reflects upon the nature and style of neotectonic activity along the ECFS responsible for the development of the basin. Interpretation of these data aid to improve our understanding of neotectonic activity in the SCCP.